The Program Project has put together perhaps the best resource file of medical data that has ever existed. The goal of the data core is to update these files and to acquire the new data resources necessary for continuing Program Project research. Many of the data resources that will be used in the Program Project are publicly available, and are managed routinely through the administrative core. Three data sets, however, involve special acquisition arrangements and supplementary costs. The specific aims of the data core are: (1) To maintain our existing longitudinal Medicare data files, to update these files with more recent Medicare data as it becomes available, and to develop linked comprehensive Medicaid data for a large sample of older Americans. (2) To maintain our existing longitudinal Medstat data files, and to obtain updated and expanded data from Medstat for analyses of health care costs in large firms. (3) To acquire comprehensive hospital discharge records for California, Florida, Massachusetts, New Jersey and New York.